Chlorobenzene hydrodechlorination on bimetallic catalysts prepared by laser electrodispersion of NiPd alloy

Abstract

Abstract NiPd bimetallic systems were for the first time synthesized by laser electrodispersion (LED) of the Ni 77 Pd 23 alloy target followed by the deposition of produced bimetallic particles on a TEM copper grid and alumina granules. Selective area energy-dispersive analysis confirms the bimetallic nature of NiPd particles deposited on a TEM copper grid. Their mean size is 1.0 nm according to TEM. XPS data demonstrate that under deposition on alumina granules (total metal content of 0.005 wt.%), nickel in bimetallic particles nearly completely oxidizes to Ni 2+ species predominantly in the form of aluminate. At the same time major part of palladium (84%) exists in Pd 0 but oxidizes to Pd 2+ (80%) during 6 months storage in air. Both metals are deposited on the external surface of alumina granules and localized in the same areas. In situ reduction of both metals by H 2 in the catalytic cell of XPS spectrometer is hindered. Nickel is not reduced even at 450°C, confirming the formation of NiAlO x , whereas palladium is reduced at higher temperatures compared to a similar monometallic catalyst. Nevertheless, NiPd/Al 2 O 3 catalyst is more efficient in gas-phase chlorobenzene hydrodechlorination at 150–350°C than Ni/Al 2 O 3 and even Pd/Al 2 O 3 , and much more stable. The difference may be caused by the formation of new active sites due to the contact between Pd 0 and NiAlO x -modified support, and the protective action of spinel reacting with HCl by-product.